At 01:29 PM 4/10/2007, Mark Hahn wrote:
>>It was PVM that enabled true message passing parallel code to be written
>>that made a pile of machines (be they Alphas, simple PCs, Sun
>>I'm not disagreeing, but wonder why PVM is basically extinct now.
>that is, why was MPI considered an improvement/replacement?
I will speculate that it's because "message passing" as a
interprocess and interprocessor communications model came around
first, and had a bit more traction. There are always those hardy
souls willing to partition the problem themselves as opposed to some
sort of magic virtual memory/machine model doing it for them.
And, there were extensive libraries to divvy up the work using a
message passing layer underneath. Why.. sitting here on a shelf in
my office (as a curiosity with which to beat young
whippersnappers/early career hires who think they've just invented
such things) is a set of lecture notes and manuals for CCLISP (ah
yes.. the glory days of LISP for everything) as well as all the math
libraries for cluster computation for matrix math, etc.
Those are all based on much earlier message passing work of the
DECnet era.. I have a textbook on distributed computing from 1980
(Weitzman, "Distributed Micro/Minicomputer Systems") which describes
all those schemes (DEC PCL-11B? IBM DPPX? TRW DDP? etc.), both shared
memory and message passing oriented (note that this book explicitly
doesn't talk about supercomputers, which, obviously, also had shared
memory/crossbars/etc). It even mentions that new-fangled experimental
interconnect from Xerox called Ethernet, although it talks about a
variety of variants that might fix some of the observed problems....
Anyway.. the message passing schemes would work over "really slow"
links (albeit at reduced performance) and would at least be
functional for decomposing a problem. I would cringe to think of
trying to do a PVM style task with 56,700 bps interconnects between
processors. Remember, you're dealing with node processors the like
of PDP11s and 1 microsecond cycle times (I'd have to drag out my
11/70 manual to see for sure).. Pushing out a megabit per second on
ANY interface would have been a chore.
James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875